1. Field of the Invention
This invention relates to constant velocity universal joints, and in particular, to a centering apparatus for a constant velocity universal joint.
2. Description of the Prior Art
Constant velocity universal joints have found wide application in automotive, agricultural, aircraft, industrial and instrument applications to couple two rotary shafts that have an angular misalignment. A particularly common type of constant velocity universal joint is the double Hooke's joint. A double Hooke's joint typically comprises a double inner housing, a pair of outer yokes, a pair of cross links with each cross link pivotally connecting one of the outer yokes to one of the ends of the double inner housing, and a centering apparatus for connecting the two outer yokes to one another. The drive shaft is connected to one of the outer yokes and the driven shaft is connected to the other outer yoke. The centering apparatus operates to equalize the angles between the drive shaft, the driven shaft, and the axis of the double inner housing to provide a constant velocity ratio between the drive and the driven shaft.
One type of centering apparatus is disclosed in Carrier French Pat. No. 818.717, published Oct. 2, 1937. This type of centering apparatus comprises a centering plate which is guided within an annular raceway intermediate of the outer yokes. A tubular recess defining means extends axially through and on each side of the centering plate. A pair of blocks are slidably received within the recess and each block slidably receives a ball-head extension of the adjacent yoke to provide a connection between the outer yokes through the centering member.
Although the centering apparatus disclosed in French Pat. No. 818.717 provides surface contact, the prior art has a number of disadvantages. For example, the tubular recess defining means abuts the inner periphery of the annular raceway to limit the angular misalignment of the drive and driven shafts. Since the outer diameter of the tubular recess defining means is the limiting factor, a relatively large outer diameter of the tubular recess defining means requires a relatively large diameter double inner housing. However, a large diameter double inner housing causes vibration and poses a safety hazard which is undesirable.
Another problem is that the ball-head extensions are susceptible to failure. The ball-heads are joined to the outer yokes by a small radius fillet to allow clearance between the tubular recess defining means and the ball-head extensions in extreme positions. This small radius creates a stress concentration which can cause stress hardening and embrittlement at the base of the ball-head extension. Consequently, the ball-head extensions limit the life of the joint.
Another problem is that the centering apparatus in constant velocity universal joints is subject to great stresses and an extremely harsh environment particularly in agricultural applications. To provide for smooth and efficient operation under these circumstances, lubrication is required to reduce the friction within the centering apparatus. However, the prior art has not provided a dynamic lubrication system contained within the centering apparatus. Therefore, a need exists for a compact constant velocity universal joint with a durable centering apparatus.